1. Field of the Invention
The invention relates generally to hand-held pipetting devices and more specifically to a hand-held pipetting device having a housing, a pipette receptacle coupled to the housing for a replaceable pipette, the replaceable pipette received with a first end in the pipette receptacle and having a tip at a second end, a negative pressure source for aspirating a liquid, an overpressure source for dispensing an aspirated liquid, an air line which connects the negative pressure source and overpressure source with the pipette receptacle, a valve system which is at least partially electrically controllable and which is arranged within the air line, an aspirating button coupled to the housing, a dispensing button and a light source.
2. State of the Art
Precise measuring of liquid volumes and transferring a precisely measured liquid volume from a first container into a second container are worldwide one of the most frequent work steps in chemical and physical laboratories. The use of so-called Peleus balls as a pipetting aid is standard in laboratories. After the Peleus ball is attached to a conventional graduated pipette, the air contained in the ball has to be ressed out by means of a ball arranged opposite to the pipette.
By actuating two further ball valves, the liquid level can be raised or lowered. A disadvantage of the Peleus ball is the possibility that liquid can accidentally be sucked into the ball thereby contaminating the same. A further disadvantage is that for operating the ball valves, the thumb and a further finger of the hand is necessary and that operating the ball valves requires a sensitive motor system.
In laboratories, also other constructions are used for safe measuring of liquids. Ergonomic and safe pipetting aids are hand-held pipetting devices into which the serological pipettes are inserted. The pipetting speed can be adjusted in an infinitely variable manner by means of a knurled screw. By pressing the upper dosing button, liquid is aspirated in a controlled manner. A lower dosing button serves for precise dispensing of the liquid, which can also be done drop-by-drop. A sterile filter arranged within the pipetting head prevents contamination. Said pipetting aids are operated with electrical power, in particular by a rechargeable battery. The operating time of such hand-held pipetting devices is limited by the relatively high power requirement of the suction device.
The withdrawal of liquid from containers demands intensive concentration, in particular in case of an optical impairment because, e.g. the containers are made of colored glass or are completely opaque. In this case, on the one hand, it is difficult to detect if the tip actually immerses into the liquid and, on the other hand, the scale on the pipette is difficult to read. In particular in deep containers with a low liquid level, the withdrawal of accurate liquid volumes is complicated and stressful. These disadvantages apply also to draining liquids from the pipette into the above described containers where, for example, contact between a container and the pipette tip is to be avoided.
From U.S. Pat. No. 5,919,706, a pipetting device is known which is equipped with a system for measuring the height of a liquid level. The system comprises a light source and a light-transmitting fiber connected to the light source, at which fiber the light exits in a focused manner in the form of a thin measuring beam. The light-transmitting fiber is arranged in the lower region of a nozzle onto which a replaceable pipette tip can be attached. For the quality of the measurement, a clear and precisely focused light signal is necessary. The lower end of the light-emitting body in the shape of a convergent lens serves for focusing the measuring beam. The outgoing light is reflected on a liquid surface and, depending on the height of the liquid level and the properties and condition of the liquid, partially absorbed therein. In contrast to the outgoing light, the reflected light has a weaker intensity. The intensity difference between the incoming and the outgoing light beam serves for generating an electrical measuring signal.
The outgoing light beam acts as a contactless measuring beam and is specifically adapted to this task. Thus, the used light is completely unsuitable to take over other tasks such as, for example, the illumination of the environment of the pipette or the pipette scale. The advantage of the described pipetting device is that the height of the liquid level is displayed to the user. A disadvantage is, however, that the pipetting device is relatively expensive to manufacture due to the additional measuring system.
The present invention avoids the described disadvantages. A hand-held pipetting device is to be provided, the handling of which requires less concentration so that, e.g., unintended suction of air, because the pipetting tip can not be seen, can be avoided. The hand-held pipetting device is to be constructed in a particularly simple and cost-effective manner. In addition, reading the measuring scale on the pipette is to be simplified. Another aim is that the power requirement of the proposed hand-held pipetting device is as low as possible.